Field of the Invention
The invention relates generally to antennas and, in particular, to antennas for receiving GNSS signals and Irridium and/or Inmarsat signals.
Background Information
Devices that utilize GNSS satellite signals for position determination may also utilize Irridium and/or Inmarsat signals for two-way communications. Further, the Irridium and/or Inmarsat signals may provide GNSS differential and satellite correction information that is utilized, in a known manner, along with the GNSS signals for precise position determination. For convenience, the term “Inmarsat signals” is used hereinafter to refer singly and collectively to the Irridium and/or Inmarsat signals.
The Inmarsat signals are transmitted from satellites that have geostationary orbits at the equator. The GNSS signals are transmitted from satellites that are not geostationary but instead circle the earth in predetermined paths. The Inmarsat signals arrive at an Inmarsat antenna at azimuth angles that correspond to the distance of the antenna from the equator while the GNSS signals arrive at a GNSS antenna at azimuth angles that change throughout the day as the respective GNSS satellites circle the earth. The frequency bands of the GNSS signals and the Inmarsat signals are relatively close and both types of signals are right-hand-circularly-polarized (RHCP). Accordingly, known prior systems may utilize a single antenna for both signals, though the signal quality of particularly the Inmarsat signals is adversely affected since the antenna is not typically optimized for the Inmarsat signals.
Separate conventional GNSS and Inmarsat antennas may be utilized for the GNSS and the Inmarsat signals. The antennas are, however, likely to be placed in relatively close proximity to one another. Accordingly, the two antennas will thus interfere with one another, such that signal quality at the respective antennas is adversely affected. Further, the use of the two conventional antennas adds bulk to the devices, which like many consumer devices are getting smaller in size.